Process gas cleaning

Wet chemical processes A gas-cleaning process that uses certain chemicals to ensure the maximum retention of a given pollutant in the cleaning fluid. 

Emission control the use of gas cleaning processes to reduce emissions. 

When coal is burned in a combustion unit, mineral matter undergoes major changes that lead to problems of clinker formation, fly ash, slagging, and boiler tube corrosion. The efficiency of a combustion unit is related to the amount of ash produced, since it is a diluent. On the positive side, ash has been utilized as a construction material and is a possible source of refractory materials, as cement additives, or as adsorbents for gas-cleaning processes. However, the composition of the ash must be known before it can be utilized in this way. 

A mixture of humid air and sulfur dioxide forms the model gas for these experiments, as in today s world the removal of sulfur dioxide from exhaust gases is an important gas cleaning process. Calcium hydroxide suspension was injected as a reactant, and the experimental investigations have been subdivided into two parts. 

Chevalier, J., Rousseaux, P., Benoit, V, and Benadda, B., Environmental assessment of flue gas cleaning processes of municipal solid waste incinerators by means of the life cycle assessment approach, Chem. Eng. Sci, 58, 10 (May) 2053-2064, 2003. 

Rensfelt, Erik, and Ekstroem, Clas. Fuel gas from municipal waste in an integrated circulating fluid-bed gasification/gas-cleaning process, Energy Biomass Wastes, No. 12, pp. 891-906 (1989). 

Rensfelt E. Ekstrom C. (1989) Fuel Gas from Municipal Waste in an Integrated Circulating Fluidized bed/Gas Cleaning Processes. Energy Biomass Wastes, 12, 811-906. 

The slag is regarded as resistant to elution. Because of this and because of its glassy nature and high density the slag is more highly valued than the ash from the incineration process. The latter has to be disposed off if it cannot be fractionated by suitable measures in the off-gas cleaning process. 

More recently, a trend has been observed in many countries over the past decade, which moves in the direction of less complex, integrated flue gas cleaning processes. This simplification in the number of flue gas cleaning process elements means, as a rule, that it is no longer feasible or viable to recycle the treated products from flue gas cleaning into the economic trading cycle. 

Thus, while industry marches on using many of the same processes that were in use in the early days of the centmy, more stringent methods for cleanup are necessary before any product/by-product can be released to the atmosphere. And this is where gas processing becomes an important aspect of industrial Ufe. Furthermore, gas-cleaning processes are now reqnired to be more efficient than ever before. 

Thns, the gas-cleaning process must always be of optimal design for both the upstream and downstream processes. 

The basic principles of some generally accepted gas cleaning processes for solvent removal are given in Table 22.1.2. For more than 70 years adsorption processes using activated carbon, in addition to absorption and condensation processes, have been used in adsorptive removal and recovery of solvents. The first solvent recovery plant for acetone was commissioned for economic reason in 1917 by Bayer. In the decades that followed solvent recovery plants were built and operated only if the value of the recovered solvents exceeded the operation costs and depreciation of the plant. Today sueh plants are used for adsorptive purification of exhaust air streams, even if the return is insufficient, to meet environmental and legal requirements. 

The gas cleaning process was developed by RENET, Austria. It operates in three stages. Eine hydrated lime is first injected into the system to reduce the tar content to less than 1 g/Nm, accompanied by enhanced recovery of sensible heat from the product gas stream ... 

Process Intensification for Sustainable Energy Conversion Table 11.2 Classification of gas cleaning processes... 

Figure 11.18 Scheme of the gasification-gas cleaning process Two monolith layers reactor utilizing commercially produced ni monoliths, coupled with a pilot-scale gasifier. fSource Reproduced with permission from Ref [92]. Copyright 2006, American Chemical Society)... 

Diaz-Somoano, M. and Martinez-Tarazona, M.R. (2005) Retention of zinc compounds in solid sorbents during hot gas cleaning processes. Energy Fuels, 19, 442 46. 

A variety of waste gas cleaning processes " are commercially available. They are used to remove organic vapors (solvents) from air emissions from various industries and product lines. The main applications of solvents in various industries are given in Table 22.1.1. 

LCA have been successfully utilised in the field of plastics waste management, for example, to assess differences in environmental performance between different waste incineration strategies [24] or related activities such as the flue gas cleaning process of plastic waste incinerators [25], to compare the environmental performance of different scenarios for the management of mixed plastics waste as well as that of specific plastic waste fractions [25-32]. 

Another well-known gas cleaning process is adsorption. Kohl and Nielsen reported on H2S adsorption on molecular sieves at temperatures between 25 and 150°C [21]. Low H2S pressures, corresponding to 1300ppm H2S at 1 bar, are only possible for lower temperatures. Under these conditions, the maximum H2S loading amounts to 0.05 g H2S per gram of adsorbent. 

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